Lets talk some physics here...

[SDmtnbkr]

Disclaimer: I know nothing about physics.

The more mass an object has the longer it takes to heat up. However, if an object has less mass but heat is allowed to escape, or bypass it, it will take too take longer to heat up. Knowing this, which type of handguard/rail would take longer to heat up; a beefy rail like the Geissele rails, or a super light rail with lots of vents cut out like the Bootleg (PWS & Rebel Arms) rails? Another factor would be time to cool down.

Taking it a step further, how does the barrel play into this? Will a pencil barrel not be able to hold on to the heat and pass it on to the rail, therefore heating it up quicker than a heavier profile barrel?


**I posted this here because it is relevant to building an AR rifle if you care about not fusing your skin to the rail, and don't want to stash gloves next you gun. ...."excuse me bad guys, can you give me a second to put my gloves on". And yes, I know you're not getting into a 2hr TIC in your house, justing trying to drum up some discussion here. ....but feel free to move it if you think it should go somewhere else.

[Lonestargrizzly]

Can't use a vertical or angled foregrip?

[SDmtnbkr]

Can't use a vertical or angled foregrip?

Nope, that's not really in the spirit of the discussion..... say AR Pistol.

[Lonestargrizzly]

Nope, that's not really in the spirit of the discussion..... say AR Pistol.

What about rail covers?

[russ69]

The standard A2 handguard is a good insulator, an aluminum rail is a good conductor. The calculation is complicated enough that it would be easier to make measurements than to do the calculation.

[thetruecheese]

What heats up more: A cast iron frying pan,. or a lighter steel cookware?

I find both are too hot. So i use a potholder.

Where are your handgaurds?

[SloChicken]

Some factors in play

1. Mass of material

2. Specific heat of material

3. Humidity or particle pressure (conductive and convective energy tx)

4. Wind - convective tx assoc with ambient environment (e.g., wind chill)

5. Surface area of material. (Radiant, convective, conductive)

I am sure there is more, including fluid dynamics aspects of the little holes in the handguard.

If I were you I wouldn’t overhink it, unless you like math and headaches. I would just find something that is sturdy and you like the looks of, and be done with it.
Spend that time drinking a beer instead.

[BearJesus2012]

Hmmm, lets see.

Pencil barrel, Medium, and Heavy. The Barrels act like insulators and will retain the heat longer the thicker they are. Barrels do not cool like most think, airflow is useless, they essentially radiate the heat out of the center... fluting is useless for cooling too from a surface area standpoint. A fluted barrel will cool faster because the heat has less material to pass through.

I have personally had heat issues with the old plastic hand guards. I would be very surprised to find that in the use case you mentioned, heat would become an issue. I have had heat issues on free float rails during carbine classes but that was extensive firing and the sun was beating down on us. My friend with a non-black AR15 had no issues (same rail).

The rail will heat up and pass the heat along again through radiation. So your best bet would be plastic rail covers on the rail to stop any heat transfer.

The lighter material hand guard will get hotter faster and colder faster. The thicker one will retain more heat longer but take longer to heat up. Fun thought experiment!

[SloChicken]

What heats up more: A cast iron frying pan,. or a lighter steel cookware?

I find both are too hot. So i use a potholder.

Where are your handgaurds?

LOL,

The truth,

Best said with few words.

[SDmtnbkr]

What about rail covers?

Negated because they both could have covers or not at all.

The standard A2 handguard is a good insulator, an aluminum rail is a good conductor. The calculation is complicated enough that it would be easier to make measurements than to do the calculation.

Oh god, I would sooner pluck out my eyes than deal with those damn A2 handguards again. I may be high speed low drag now, but I deployed to Iraq with iron sights and A2 handguards... twice.

[SDmtnbkr]

I think everyone's missing the point.... I'm not asking for help to build a rifle, just trying to spark some interesting conversion here beacuse I recently had to make this same choice. Just figured I'd see what everyone else thought.

After a day of heavy shooting my KMR might as well have been a branding iron, even with rail covers. The metal is thin and the design does not allow hot air to vent well. My brake is pinned and welded, so I'm stuck, accept for the fact that that Bootleg (PWS) rail used the KMR mounting hardware and barrel nut, so I'm switching to that. For my 8" 300blk, I'm switching to the Geissele because my mini KMR lights up even faster. The Geissele has wider points in the middle, so with rail scales, my hands will be far more protected than with a typical slim keymod rail.

[SDmtnbkr]

Hmmm, lets see.

Pencil barrel, Medium, and Heavy. The Barrels act like insulators and will retain the heat longer the thicker they are. Barrels do not cool like most think, airflow is useless, they essentially radiate the heat out of the center... fluting is useless for cooling too from a surface area standpoint. A fluted barrel will cool faster because the heat has less material to pass through.

I have personally had heat issues with the old plastic hand guards. I would be very surprised to find that in the use case you mentioned, heat would become an issue. I have had heat issues on free float rails during carbine classes but that was extensive firing and the sun was beating down on us. My friend with a non-black AR15 had no issues (same rail).

The rail will heat up and pass the heat along again through radiation. So your best bet would be plastic rail covers on the rail to stop any heat transfer.

The lighter material hand guard will get hotter faster and colder faster. The thicker one will retain more heat longer but take longer to heat up. Fun thought experiment!

Ahh now here's a good response.... the barrel heat radiation concept is great info, I never really thought about it like that. The metal is so dense, airflow won't really affect it? You kind of contradict yourself on the fluting though. I thought fluting helped with cooling because it creates more surface area to allow to air to cool it faster. Is this not the same concept with fins on high powered electronics, or now, high end shock absorbers like King Suspension?

ETA: I wonder if some of the high temp heat resistant coating could be applied to the inside of the rail? Something like a high temp ceramic coating used in race cars. This would not allow the rail to absorb the heat and it would just pass through. hmm...

[Walking Fire]

Space Shuttle Heat Shield Hand guards are the only way to go..

[Nguyen]

Nope, that's not really in the spirit of the discussion..... say AR Pistol.

Slap a grip on that b*tch

Old pic, spent all my money on call of duty stuff... i couldnt afford dust cover or forward assist.

OAL >26 inches :O

[mif_slim]

It depends on how much you're planning to shoot. My good ol'quad rails took much longer to heat/cool and I noticed I shot longer throughout the day than my newer lighter, faster, more operator, slim rails.